Vapor fractometers



Oct. 2, 1962 N. BRENNER 3,056,277

VAPOR FRACTOMETERS Filed March 5, 1959 FIG. l

| 26 i I 1 24 I2 I4 I I6 22 ID OXYGEN AND I NITROGEN l8 2 (SILICA GEL)2I REE 28 30 sans l L. MEASURING 32 34 n NITROGEN 36 (SYNTHETIC ZEOLITE)CARBON DIOXIDE (SILICA GEL) F I G. 2 OXYGEN (SYNTHETIC ZEOLITE) START INVEN TOR.

NATHAMEL BRENNER BY WK ATTORNEY United States Patent O 3,056,277 VAPORFRACTOMETERS Nathaniel Brenner, South Norwalk, Conn., assignor to ThePerkin-Elmer Corporation, Norwalk", Conn., a corporation of New YorkFiled Mar. 5, 1959, Ser. No. 797,370 2 Claims. (Cl. 73-23) Thisinvention relates to vapor fractionation and more particularly to aunique vapor fractometer apparatus which produces improved analyses.

Vapor fractometry, also known as vapor fraction chromatography, is awell-known analytical method for the analysis of multi-componentsamples. Two methods are most widely used for vapor fractometry. One ofthese is known as the clution-adsorption method, and the other is knownas the elution-partition method of separation. In both methods a vaporsample is injected into a carrier gas, and the combination is thenpassed through a column containing a separating material. The materialcontained in the column slows the rate of progress of the differentcomponents of the sample by varying amounts, so that the carrier gas asit exits from the column contains bands of the various components of thesample. The columns which are used in chromatographic apparatus may beof several typesfor example, the well-known packed column and a newercoated column which comprises a tube having its internal surface coatedwith the separating material. The separating material may be eitherliquid or solid-alone, as in the coated tube, or in combination withvarious supporting materials.

Although vapor fractometry, as pointed out above, is a widely used anduseful analytical procedure, there are certain problems which, up untilthe present time, have not been solved. One of these problems relates tothe complete separation of all the components which may exist in a givensample. For example, many gas samples contain oxygen, nitrogen, andcarbon dioxide and it is often desired to measure the concentration ofeach of these components in a sample. However, oxygen, nitrogen andcarbon dioxide cannot be resolved in any system of single columns orcolumns in series unless highly cumbersome temperature programmingsystems o extremely long elution times are employed. The reason for thisis that nitrogen and oxygen can be resolved only on powerful adsorbentswhich have excessive retention characteristics with respect to carbondioxide. The only materials which separate oxygen from nitrogenconveniently at room temperature are synthetic zeolites of the typecommercially known as Molecular Sieves. These materials, however, adsorbcarbon dioxide irreversibly. Similarly, there are several adsorbentswhich will separate oxygen and nitrogen from carbon dioxide-silica-gel,for example.

Another problem which the apparatus of the prior art has failed to solverelates to the measurement of exact sample size. In vapor fractometrythe small quantity of sample required makes the accurate metering ofsamples into the instrument quite ditficult. The size of the sample mustbe accurately known, however, in order to calculate percentages ofcomponents in the total sample. One approach to this problem which hasbeen attempted is the development of accurate metering devices to injectprecise amounts of sample. Such devices are complicated and expensiveand must be precisely calibrated.

The primary object of this invention is to provide an apparatus capableof accurately separating and analyzing heretofore difiicultly separablecomponents of a sample mixture. Another object is to provide ameasurement system in the vapor fractometer itself which reflects theamount of sample injected by ordinary sampling methods.

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The above objects are achieved by providing a vapor fractometer forseparating a sample into its constituents in accordance with theirphysical characteristics. The fractometer comprises a source of carriergas and means for introducing the sample into the carrier gas. At leasttwo columns are provided having a common inlet in series flowrelationship with the carrier gas path. The columns define parallelpaths for the How of carrier gas and sample and at least one of thecolumns contains material for which the components of the sample havedifferent afiinities. In the embodiment herein described the detectionmeans are then provided in series with the common outlet of the parallelcolumns for measuring the concentrations of the components present inthe carrier gas. It is understood that the term parallel as usedthroughout this specification means functionally parallel and notnecessarily physically parallel.

FIG. 1 is a drawing in schematic form of one embodiment of the presentinvention and FIG. 2 is a Fractogram of an example of an analysisemploying the present invention.

The apparatus of the present invention will be more readily understoodby reference to the drawing which shows in schematic form apparatusembodying the present invention. In the diagram a source 10 of carriergas is illustrated in combination with a gas regulator 12 for providinggas to a conduit 14. Conduit 14 divides into two branch conduits 16 and18. Conduit 18 conducts carrier gas to the reference side of detector21. Conduit 16 conducts the carrier gas to parallel columns 20 and 22. Asample is injected into the carrier gas at sample injection point 24.Variable flow restriction elements 26 and 28 are provided in each ofcolumns 20 and 22 for the proper apportionment of the gas flowtherebetween. Thus, the rate of gas flow through column 20 is controlledby restriction element 26 independently of the rate of gas flow throughcolumn 22 controlled by element 28. As a result it is readily understoodthat the time relation of the eluted bands from columns 20 and 22 may beseparately regulated and adjusted so that the bands of each can be timedisplaced in a predetermined order. This is considered to be aparticularly novel feature of the present invention. The outlets ofcolumns 20 and 2 are joined at point 30 and are connected by conduit 32to the sensing cell of detector 21 and from there to an appropriatevent. A measuring circuit 34, such as a Wheatstone bridge, develops anoutput voltage which varies according to the difference in certainphysical characteristics between the gases in the reference and sensingcells of detector 21. This difference is transmitted to recorder 36where it is recorded as the percentage of a given component in thesampling mixture. By providing a vapor fractometer having at least twocolumns in parallel relationhip, it has been found possible to analyzequickly and accurately mixtures containing components which heretoforehave been quite difficult to separate.

As an example of the present invntion, a one meter column was packedwith silica-gel, a two meter column was packed with a synthetic zeoliteand the two columns placed in parallel in a standard vapor fractometer.A gaseous sample comprising oxygen, nitrogen, and carbon dioxide wasinjected into the inert carrier gas. That part of the sample whichpassed through the column containing silica-gel was separated into twoparts-oxygen and nitrogen appearing as one band and carbon dioxide asthe second. That portion of the sample which passed through the columncontaining the synthetic zeolite was separated to yield an oxygen bandand a nitrogen band. The carbon dioxide was irreversibly held by thelatter column. An excellent analysis was obtained wherein separate,distinct peaks were recorded for carbon dioxide and nitrogen without thenecessity of complex switching 3 arrangements. The particular timerelationship of the bands passing to the detection apparatus iscontrolled by flow restrictors 26 and 28 to avoid any undesirableoverlap and confusion of the bands. The resu ts of the above example areillustrated in FIG. 2. Any other combination of adsorption andpartitioning agents may also be used in the columns of such a parallelsystem. 'For example, a separation of oxygen, nitrogen, carbon monoxide,methane, and higher hydrocarbons up to C, may be etfected in one samplerun by placing a synthetic zeolite for the separation of oxygen,nitrogen, methane and carbon monoxide in parallel with a standardpartition column containing dimethylsulfonane for the separation of theC; to C, fractions. Quantitative measurements of the foregoing analysesare obtained by calibration using known standards under identicalconditions.

This invention is also suited for the analysis of gaseous samples whenemploying the small-diameter internallycoated columns known to the artas capillary columns. Columns of this type are described by Marcel J. E.Golay in an article entitled, Theory and Practice of Gas-LiquidPartition Chromatography With Coated Capillaries," appearing in the bookGas Chromatography published in 1958 by Academic Press Incorporated.Such a column may be used in this invention either in parallel with asimilar column, or with a standard packed column.

As an example of yet another feature of the parallel column invention, aseparation column may be provided in parallel with a non-separatingcolumn. The non-separating column would thereby provide a single peakreadout having an area proportional to a fixed percentage of the totalsample. This area could then be used as the basis for internalnormalization calculation. Thus a standard sampling method may beutilized, although only a very small portion of the sample taken wouldbe actually passed through the adsorption column.

It will be apparent to those skilled in the art that the invention asdescribed herein has wide applicability in vapor fractomeu'y. Althoughonly two analyses have been described, it will be understood that theparallel column system is practically unlimited in usefulness and, byproper selection of adsorbents, many different sample mixtures may bequickly and accurately analyzed.

It is of course understood that the embodiment above described andillustrated in the drawings is by way of example and variousmodifications could be made without departing from the spirit and scopeof the present invention. For example, various arrangements of detectionapparatus could be connected to the outlet ends of the columns.

I claim:

1. A vapor fraetometer for separating a sample into its constituents inaccordance with their physical characteristics comprising a source ofcarrier gas; means defining a path for said carrier gas; means forintroducing a sin gle sample into said carrier gas; at least two columnshaving a common inlet in series flow relationship with said pathdefining means, said columns defining parallel paths for thesimultaneous flow of said carrier gas and sample, eachof said columnscontaining a diflferent material for which the components of the samplehave different afiinities; flow control means adapted to control therelative flow rates between said columns; and detection means in seriesflow relationship with the outlets of said parallel columns formeasuring the concentrations of said components in said carrier gas.

2. A vapor fractometer for separating a sample into its constituents inaccordance with their physical characeristics comprising a source ofcarrier gas; means defining a path for said carrier gas; means forintroducing a single sample into said carrier gas; at least twochromatographic separating columns having a common inlet in series flowrelationship with said path defining means, said columns definingparallel paths for the simultaneous flow of said carrier gas and sample,each one of said columns comprising a tube internally coated with adifferent substance for which the components of the sample havedifferent afiinities; flow control means adapted to control the relativeflow rates between said columns; and detection means in series flowrelationship with the common outlet of said parallel columns formeasuring the concentrations of said components in said carrier gas.

References Cited in the file of this patent UNITED STATES PATENTS2,728,219 Martin Dec. 27, 1955 2,868,011 Coggeshall Jan. 13, 1959FOREIGN PATENTS 1,170,329 France Jan. 13, 1959 OTHER REFERENCES Apublication entitled, Vapor Fractometry (Gas- Chromatography), by H. H.Hausdorff of the Perkin- Elmer Corporation, published in June, 1955.

An article entitled, Design Considerations of a Gas ChromatographySystem Employing High Efliciency Golay Columns by Richard D, Condon inAnalytical Chemistry, vol. 31, No. 10, October, 1959, only page 1717applied and referring to Golay, Symposium on Gas Chromatography,Amsterdam, Holland, 1958.

An article entitled Two-Stage Gas-Liquid Chromatography by Simmons etal. in Analytical Chemistry, vol. 30, No. 1, January, 1958, pp. 32-35.

The text entitled, Vapour Phase Chromatography" by D. H. Desty, 1957,Pp. 332-333.

